The present invention relates to a process for the production of cyclohexanol, cyclohexanone and cyclohexyl hydroperoxide from a cyclohexane oxidation process.
Oxidation of cyclohexane by air produces a reaction product comprising cyclohexanol (A), cyclohexanone (K) cyclohexyl-hydroperoxide (CHHP) and small amounts of by-products. The reaction product is treated with water followed by separation of organic and aqueous phases. The organic phase comprising A, K and CHHP is further treated to cause decomposition of CHHP to K and A. Therefore, K and A are the main product of the overall process, their mixture is commonly known as xe2x80x9cKA-oilxe2x80x9d.
Several byproducts formed during the above processes remain as impurities mixed with KA oil (crude) along with unreacted cyclohexane. Refined KA oil is produced from crude KA oil by distillation. All the byproducts, catalysts, additives, corrosion derived metal compounds form what is referred to as the xe2x80x9ctailsxe2x80x9d of the distillation column (U.S. Pat. No. 4,720,592). In order to eliminate the by-products produced during the process, the KA oil is distilled in the final step. The material that remains after the KA distillation is a viscous material, usually dark in color, comprising the impurities formed during the process, the non-volatile catalysts, and any additives that were used in the process. Collectively these materials are referred to as xe2x80x9cNon Volatile Residuexe2x80x9d or xe2x80x9cNVRxe2x80x9d). The tails stream is often concentrated through evaporation. The concentrated stream, commonly known as non-volatile residue (NVR) is often disposed of as boiler fuel.
Corrosion in process vessels made of stainless steel adds chromium to NVR. In addition, for a CHHP decomposition process using chromium catalyst (U.S. Pat. No. 4,465,861), the chromium ends up in the NVR. Typically, a concentration of chromium in the range of 2-100 ppm is observed in NVR. Upon combustion in a boiler, the chromium forms a part of the emission through boiler stack gas. In order to comply with environmental regulations, the stack gas needs expensive treatment for chromium reduction. Alternative routes to disposal of NVR are also expensive.
It is, therefore, desirable to have process of oxidation of cyclohexane to produce KA oil, the said process comprising one or more steps to reduce chromium content of NVR so the stack gas corresponding to its combustion will contain an acceptable low concentration of chromium.
The NVR is an aqueous dispersion. Typically, the composition comprises formic acid, acetic acid, butyric acid, valeric acid, caproic acid, 6-hydroxycaproic acid, succinic acid, glutaric acid, adipic acid, phosphoric acid organic esters, chromium salts, and other materials.
The amount of NVR formed during KA production is significant, it may represent up to 20% of the amount of KA oil produced and normally it is disposed by burning and getting credit for the fuel value. Because of more demanding environmental regulations the disposal of NVR with high chromium content by burning in boilers will be unacceptable.
There are known procedures to eliminate hexavalent chromium from heavy metal sludge or waste liquid, involving reducing the hexavalent chromium in acidic solution to trivalent (JP 2001058192 A 20010306). This procedure is not applicable for Cr elimination from NVR because all the NVR will be solubilized during treatment in water.
There are also treatment systems available to eliminate chromium from plating operations (U.S. Pat. No. 5,932,109) by precipitating using hydrazine or Al and Cu shavings (RU 2,023,674) by adding calcium hydroxide to specified pH value then barium hydroxide to further increase pH (SU 1323537).
The object of the present invention is to provide a method for producing KA oil and having NVR by-product with low Cr concentration.